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FLYING TELESCOPE

The shimmer of the earth's atmosphere is the largest obstacle to astronomical observations. Due to this fact, aircraft have been used for years as platforms for telescopes. American astronomers have worked with NASA´s Gerard P. Kuiper Airborne Observatory (KAO) for more than a decade. The airborne observatory made some significant observations possible, such as the discovery of the rings around Uranus and the observation of the Halley comet. However, the Lockheed C-141 Starlifter and its 90-centimeter telescope were put out of service just recently. NASA in cooperation with the German DARA is now planning a Stratospheric Observatory For Infrared Astronomy (SOFIA) as a replacement.

SOFIA will consist of a 2,5 meter long telescope which is designed for the infrared spectral range and which will be integrated into a Boeing 747SP. The first flight of this new astronomy aircraft is scheduled for the year 2000.

A major part of this new project's infrared telescope will be built by Carl Zeiss in Germany; the 2,7 meter main mirror will be casted out of Zerodur glass ceramics by Schott, another German company. The instrument´s spectral range extends from 300 up to 1600 nanometers, from visible light far into the infrared spectral range.

The biggest technical challenge is the stabilization and alignment of the airborne telescope to an accuracy of 0,2 arc seconds, even during turbulences at high altitude. A special fixture will be developed for this purpose, along with an especially precise orientation system that stabilizes the telescope and absorbs detrimental movements.

The SOFIA telescope is supposed to have ten-times the sensitiveness and a three-times better angular resolution than the 90 centimeter telescope which was used with KAO.

As of now, it is planned to use the SOFIA telescope aircraft for 160 missions per year, each lasting about seven hours with the aircraft flying at an altitude of more than 13 kilometers, above the detrimental effects of the atmosphere. 99 percent of all harmful factors, mainly the water vapor in the atmosphere, can be eliminated by doing so.

SOFIA will be based at the Moffett Field of NASA´s Ames Research Center near San Francisco. The system is supposed to remain in service for at least 20 years.

Approximately 50 teams of scientists from the USA, with international and especially German participation, will be in charge of the project and will establish observation programs. The system will not only be used for the long-term research of stars, planets, and nebulas. The airborne telescope´s major advantage is its flexibility. It can be employed on short notice for the observation of sudden appearing astronomical phenomena, for example supernova explosions or comets which may pass our planet.

From page 37 of FLUG REVUE 10/96